Ceramic sliding or sealing elements are known. Such components must satisfy a wide range of requirements depending on how they are used, to mention only resistance to corrosion by aggressive media, resistance to thermal shock due to temperature changes in the media, and resistance to wear by media containing abrasive components. The materials heretofore proposed for sliding elements, such as hard metal, aluminum oxide, infiltrated or reaction-bonded silicon carbide and monophasic silicon carbide, have been able to satisfy no more than part of the list of requirements. For example, the hard metals have the disadvantage of corrosion and weight. Aluminum oxide is extraordinarily sensitive to thermal shock. Silicon carbide infiltrated with silicon fails when used in lyes which are important in the chemical industry. Monophasic silicon carbide makes it difficult to control the surface bearing portion of the functional surface.
Italian patent application 67 746 A/82 describes a sealing disk of silicon carbide which is combined with another disk of lesser hardness to achieve a reduction of friction.
West German Patent 35 09 572 discloses sliding elements in which a substrate of oxidic or nonoxidic ceramic is provided on its functional surface with coatings of oxides, carbides, nitrides or borides, these coatings having been applied by means of chemical or physical vapor deposition processes (CVD or PVD).
These matched pairs of sliding or sealing elements have failed to achieve any importance in practice, either because in the proposal of the Italian patent application the combining of different functional surfaces causes an undesirable surface alteration of the less hard surface, or because the sliding elements made in accordance with the proposal of West German Patent 35 09 572 do not allow economical mass production on account or the expensive CVD of PVD coating processes.